Shadowplay is actually a screen recording software, but what is does is record the visual stream, the user interfaces that are being shown on screen and the output stream of the graphic card is actually the thing that is being recorded. Graphic card which is actually a processor ( gpu,graphical processng unit) which is sharing the stream with the cpu, shadowplay's process is running in cpu while gpu is processing the graphics only.. All that cpu does is just get the output stream that is being sent by graphic card and stores it in the form of a video. Hope it clears the concept